Braking force control system for vehicle

ABSTRACT

In a vehicle having an ABS control system, a braking control of a right and left rear wheels can be independently carried out when a lateral acceleration exceeds a lateral acceleration value set beforehand. When the ABS control is operated at one of the right and left rear wheels, the control system executes a stepwise pressure increase control which provides a stepwise pressure increase for the other rear wheel up to a braking pressure to be reached at a start of the control.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a braking force control systemof a vehicle which adequately distributes the braking force in braking.

[0003] 2. Description of the Related Art

[0004] In recent years, there have been proposed various braking controlsystems which make use of constitutions of anti-lock braking systems(ABS) and control distribution of braking force in normal braking to bemore adequate one.

[0005] For example, in JP-A-10-119744, there is disclosed one whichindependently increases, decreases or holds braking oil pressure of eachof right and left rear wheels when deceleration of a vehicle reaches aspecified value and when a vehicle speed exceeds a specified speed, sothat braking force distribution between rear and front wheels becomes anapproximately ideal one to perform independent braking control forcarrying out sufficient braking.

[0006] Incidentally, in the ABS control and the braking forcedistribution control as described above which provide an independentbraking for the rear wheel side, because of not so large transfer of avertical load between the right side and left side wheels in a normalturning of the vehicle, an attitude of the vehicle does not changelargely in rolling even when the brake is operated, so that the brakingcan be performed with a normal feeling of the rolling. However, in ahigh lateral acceleration turn on a high friction road, when the ABScontrol and braking force distribution control of the rear wheels areindependently carried out, because of a large difference between theright and left vertical loads, there is a fear that unpleasant rollingbehavior of the vehicle body is occurred due to change in breaking forceof the turning outside rear wheel caused by each of the brakingcontrols.

SUMMARY OF THE INVENTION

[0007] The present invention was made in view of the above with anobject of providing a braking force control system of a vehicle whichcan carry out natural, reliable and stable braking without anyparticular addition of complicated mechanisms by preventing theoccurrence of unpleasant rolling behavior. When a vehicle turns with ahigh lateral acceleration, the braking of each of the right and leftrear wheels is independently controlled.

[0008] In order to achieve the above object, according to a first aspectof the present invention, there is provided a braking force controlsystem of a vehicle, having: a lateral acceleration detecting unitdetecting lateral acceleration of the vehicle; and a braking controlunit carrying out an anti-lock braking control and carrying out anindependent braking control of right and left rear wheels, wherein, in acase that the lateral acceleration exceeds a lateral acceleration valueset beforehand, when the anti-lock braking control is operated at one ofthe right and left rear wheels, the braking control unit executes astepwise pressure increase control for providing a stepwise pressureincrease for the other rear wheel up to a braking pressure to be reachedat a start of the control.

[0009] Namely, in the above-described braking force control system of avehicle according to the first aspect of the invention, the lateralacceleration detecting unit detects lateral acceleration of the vehicle.Moreover, the braking control unit executes, when the lateralacceleration exceeds a lateral acceleration value set beforehand,stepwise pressure increase control which provides, when the anti-lockbraking control is operated at one of the right and left rear wheels, astepwise pressure increase for the other rear wheel up to a brakingpressure to be reached at a start of the control. Therefore, at a highlateral acceleration turning, at a turning outside rear wheel for whichoperation of an anti-lock braking control is slowed due to an increasein a vertical load, a stepwise pressure increase control is started fromthe time of operation of the anti-lock braking control at a turninginside rear wheel. Thus, even the anti-lock braking control is operatedat the turning outside rear wheel, no sudden strong braking is appliedand unpleasant rolling behavior is prevented from occurrence to allow anatural, reliable, and stable braking to be performed. In addition, thiscan be applied by changing control of normal anti-lock braking control,so that the realization thereof is allowed without any particularaddition of complicated mechanism.

[0010] Further, according to a second aspect of the present invention,there is provided a braking force control system of a vehicle, having: alateral acceleration detecting unit detecting a lateral acceleration ofthe vehicle; and a braking control unit carrying out an anti-lockbraking control and carrying out an independent braking control of rightand left rear wheels, wherein the braking control unit executes abraking force distribution control between front and rear wheels asspecified when the lateral acceleration exceeds a lateral accelerationvalue set beforehand, and when the anti-lock braking control is operatedat one of the right and left rear wheels, the braking control unit stopsthe front and rear braking force distribution control of the other rearwheel and executes a stepwise pressure increase control thereof forproviding a stepwise pressure increase up to a braking pressure to bereached at a start of the control.

[0011] Namely, in the above-described braking force control system of avehicle as the second aspect, the lateral acceleration detecting unitdetects lateral acceleration of the vehicle. Moreover, the brakingcontrol unit executes, when the lateral acceleration exceeds a lateralacceleration value set beforehand, braking force distribution controlbetween front and rear wheels as specified, and along with this, whenthe above anti-lock braking control is operated at one of the right andleft rear wheels, stops the front and rear braking force distributioncontrol of the other rear wheel and executes stepwise pressure increasecontrol thereof which provides a stepwise pressure increase up to abraking pressure to be reached at a start of the control. Therefore, athigh lateral acceleration, the front and rear braking force distributioncontrol is first carried out at the turning inside rear wheel withsubsequently started anti-lock braking control. Also in the turningoutside rear wheel, the front and rear braking force distributioncontrol is started subsequent to the turning inside rear wheel. However,when the anti-lock braking control is started at the turning inside rearwheel in the course of the front and rear braking force distributioncontrol, the front and rear braking force distribution control isstopped for the stepwise pressure increase control being executed. Inthis way, at the turning inside rear wheel, after the front and rearbraking force distribution control, the control is transferred to theanti-lock braking control. While, at the turning outside rear wheel,after the front and rear braking force distribution control, the controlis transferred to the anti-lock braking control through the stepwisepressure increase control. Thus, even the anti-lock braking control isoperated at the turning outside rear wheel, no sudden strong braking isapplied and unpleasant rolling behavior is prevented from occurrence toallow a natural, reliable, and stable braking to be performed. Inaddition, this can be applied by changing control of normal anti-lockbraking control, so that the realization thereof is allowed without anyparticular addition of complicated mechanism.

[0012] Furthermore, in the braking force control system of a vehicleaccording to the second aspect of the present invention, the front andrear braking force distribution control is started and executeddepending on a slipping condition of the rear wheel.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG.1 is a flowchart of high lateral acceleration braking controlaccording to a first embodiment of the present invention;

[0014]FIG. 2 is a schematic explanatory diagram of the whole brakingforce control system according to the same;

[0015]FIG. 3 is a flow chart of a braking control program according tothe same;

[0016]FIG. 4 is an explanatory diagram of variation in braking pressurewith time at braking at a high lateral acceleration turning according tothe same;

[0017]FIG. 5 is a flowchart of high lateral acceleration braking controlaccording to a second embodiment of the present invention; and

[0018]FIG. 6 is an explanatory diagram of variation in braking pressurewith time at braking at a high lateral acceleration turning according tothe same.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Preferred embodiments of the present invention will be explainedbelow on the basis of the drawings. FIGS. 1 to 4 shows a firstembodiment of the present invention.

[0020] In FIG. 2, the reference numeral 1 denotes a brake driving unit.The brake driving unit 1 is connected to a master cylinder 3 which isconnected to a brake pedal 2 operated by a driver. When the driveroperates the brake pedal 2, the master cylinder 3 applies brakingpressures through the above-described brake driving unit 1 to respectivewheel cylinders (a left front wheel cylinder 5 fl, a right front wheelcylinder 5 fr, a left rear wheel cylinder 5 rl, and a right rear wheelcylinder 5 rr) of four wheels (a left front wheel 4 fl, a right frontwheel 4 fr, a left rear wheel 4 rl, and a right rear wheel 4 rr), bywhich brakes are applied to the four wheels.

[0021] The brake driving unit 1 is a hydraulic unit provided with apressurizing source, a pressure reducing valve, a pressure increasingvalve and an oil pump etc. The brake driving unit 1 constitutes so as tofreely introduce the braking pressure independently to each of the wheelcylinders 5 fl, 5 fr, 5 rl, and 5 rr in response to input signals from acontrol unit 10 described later.

[0022] The respective wheels 4 fl, 4 fr, 4 rl, and 4 rr are structuredso as to have their wheel speed detected by respective wheel speedsensors (a left front wheel speed sensor 6 fl, a right front wheel speedsensor 6 fr, a left rear wheel speed sensor 6 rl, and a right rear wheelspeed sensor 6 rr). In the first embodiment, a vehicle speed V is to beobtained by calculating an average of the wheel speeds.

[0023] To the control unit 10, there are connected the wheel speedsensors 6 fl, 6 fr, 6 rl, and 6 rr, a brake switch 7 for detecting ONand OFF of the brake pedal 2, and a lateral acceleration sensor 8 as alateral acceleration detecting unit for detecting the lateralacceleration Gy of the vehicle.

[0024] The control unit 10 has a micro computer and the auxiliarycontrol circuits and, when the brake pedal 2 is stepped on to be made ON(when the brake switch 7 is made ON), executes a later described brakingcontrol program in response to the respective input signals so as tooutput a control signal to the above brake driving unit 1 for carryingout braking control of the vehicle.

[0025] The above-described braking control program, as shown in a flowchart in FIG. 3, first carries out at step (hereinafter abbreviated as“S”) 101, high lateral acceleration braking control, and at S102,carries out other (other than at the high lateral acceleration) brakingcontrol.

[0026] The lateral acceleration braking control at S101 is carried outin accordance with a later described high lateral acceleration brakingcontrol routine. According to the control at S101, when the lateralacceleration Gy exceeds a lateral acceleration value set beforehand,stepwise pressure increase control is executed which provides, when theABS control is operated at one of the right and left rear wheels, astepwise pressure increase for the other rear wheel up to a brakingpressure to be reached at a start of the control.

[0027] Moreover, the braking control at S102 is executed as, forexample, independent braking control which independently controls abraking force of each of the right and left wheels on the front wheelside depending on the slipping condition of each wheel and controls withthe rear wheel side as below depending on the lateral acceleration Gyand a longitudinal acceleration Gx (detected by a longitudinalacceleration sensor 11).

[0028] For example, a region of the lateral acceleration Gy other than ahigh lateral acceleration region (for example, a region below 6.89 m/s²)is divided into three regions (for example, regions from 6.89 to 4.41m/s², from 4.41 to 2.94 m/s², and below 2.94 m/s²). In a region with thelateral acceleration Gy being from 6.89 to 4.41 m/s², independentbraking control is carried out on the rear wheel side whichindependently controls braking forces of the right and left wheelsdepending on respective slipping conditions thereof. Moreover, in aregion with the lateral acceleration Gy from 4.41 to 2.94 m/s², when thelongitudinal acceleration Gx is below 6.87 m/s², the independent brakingcontrol is carried out on the rear wheel side. And when the longitudinalacceleration Gx is 6.87 m/s² or above, a select low control is carriedout on the rear wheel side which controls braking forces of the rightand left wheels depending on a wheel on the side with a large slippingcondition. Furthermore, in a region with the lateral acceleration Gybelow 2.94 m/s², when the longitudinal acceleration Gx is below 6.87m/s², the select low control is carried out on the rear wheel side and,when the longitudinal acceleration Gx is 6.87 m/s² or above, theindependent braking control is to be carried out on the rear wheel side.

[0029] As described above, in the first embodiment of the presentinvention, the control unit 10 is constituted with a function of abraking control unit.

[0030] The high lateral acceleration braking control routine executed atS101, as shown in the flowchart of FIG. 1, first reads necessaryparameters at S201, namely the lateral acceleration Gy from the lateralacceleration sensor 8 and an ABS control operation signal indicatingoperation or non-operation of the ABS control.

[0031] Next to this, the execution goes to S202 where comparison iscarried out between the lateral acceleration Gy and a lateralacceleration value set beforehand to be a reference for deciding thehigh lateral acceleration (for example, 6.89 m/s²) . With the lateralacceleration Gy being below 6.89 m/s², the execution just goes out ofthe routine and proceeds to S102.

[0032] While, when the lateral acceleration Gy is decided to be 6.89m/s² or above as being in high lateral acceleration running at S202, theexecution goes to S203 where decision is made as to whether the ABScontrol is operated at any one of the right and left rear wheels or not.When no ABS control is operated at any of the right and left rearwheels, the execution returns to S202. When the ABS control is operatedat any one of the right and left rear wheels, the execution goes toS204.

[0033] Here, the ABS control in the first embodiment is performed byknown control method, which performs calculations on a speed, anacceleration and a deceleration of each wheel, a simulatively calculatedvehicle body speed and the like. The simulatively calculated vehiclebody speed is a value calculated by making a decision of taking the caseas a sudden braking in which case a brake pedal 2 is stepped on and adeceleration of the wheel speed is above a specified value, by settingthe wheel speed at the time of the decision as an initial value, and byreducing thereafter the wheel speed therefrom with a specifieddeceleration. By judging from a comparison of the simulativelycalculated vehicle body speed and the wheel speed, a magnitude of theacceleration or deceleration of the wheel and the like, one of three oilpressure modes of a pressure increase, a pressure hold, and a pressuredecrease is selected when the ABS is operated. Specifically, when aslipping condition is exhibited as a result of increase in a differencebetween the simulatively calculated vehicle body speed and the wheelspeed, the braking pressure at this time is taken as an estimated ABSoperating pressure to carry out pressure reduction from the brakingpressure. The reduced braking pressure is then held and increased asspecified. When the pressure becomes the estimated ABS operatingpressure to fall in the slipping condition again, the pressure isreduced to repeat the above, for which a selected specified brakingcontrol signal is outputted to the brake driving unit 1.

[0034] With the decision made at S203 as the ABS control is operated atany one of the right and left rear wheels, the execution going to S204makes stepwise pressure increase control to be carried out whichprovides a stepwise pressure increase for the other wheel without ABScontrol operation up to a braking pressure to be reached (for example,an estimated ABS operating pressure), by finely repeating pressureincreasing and holding only at a start of the control. After thestepwise pressure increase control, the execution goes out of theroutine.

[0035] Under the above-described braking control, an example ofvariation in braking pressure with time at braking at a high lateralacceleration turning will be explained with reference to FIG. 4. In theexample, the surface condition of a road (for example, a road surfacefriction coefficient is μ) is taken as being the same on the right wheelside and the left wheel side of the vehicle.

[0036] First, a vehicle just going to be braked in turning normallybrings a turning inside wheel into a slipping condition easier than aturning outside wheel because the more vertical load of the vehicle istransferred to the turning outside wheel side. Thus, from a time t0 inthe diagram, the ABS control is operated at the turning inside wheel.

[0037] As a result, the stepwise pressure increase control is executedat the turning outside wheel from the time t0, by which a brakingpressure is increased stepwise up to an estimated ABS operatingpressure. Then, with the time reaching to a time t1, the ABS control isexecuted also at the turning outside wheel. Therefore, no sudden impactdue to a high vertical load is caused when the ABS control is operatedat the turning outside wheel to prevent the occurrence of unpleasantrolling behavior to allow a natural, reliable, and stable braking to beperformed. Moreover, this can be applied by only changing the softwareside of a conventional ABS control, so that the realization thereof isallowed without any particular addition of complicated mechanism.

[0038] Next, a description will be given of a second embodiment of thepresent invention with reference to FIG. 5 and FIG. 6. Incidentally, thesecond embodiment is a variation of the high lateral accelerationbraking control in the first embodiment.

[0039] Namely, the lateral acceleration braking control at S101 in thebraking control program explained in the first embodiment is carried outin accordance with a later described high lateral braking controlroutine. The braking force distribution control is executed betweenfront and rear wheels as specified when the lateral acceleration Gyexceeds a lateral acceleration value set beforehand. And, along withthis, when the ABS control is operated at one of the right and left rearwheels, the front and rear braking force distribution control of theother rear wheel is stopped and stepwise pressure increase controlthereof is executed which provides a stepwise pressure increase up to abraking pressure to be reached at a start of the control.

[0040] The high lateral acceleration braking control routine, as shownin the flowchart of FIG. 5, first reads necessary parameters at S301,namely the lateral acceleration Gy from the lateral acceleration sensor8 and an ABS control operation signal indicating operation ornon-operation of the ABS control, a signal indicating slippingconditions of the rear wheels (for example, differences between avehicle speed V and respective rear wheel speeds), and the like.

[0041] Next to this, the execution goes to S302 where comparison iscarried out between the lateral acceleration Gy and a lateralacceleration value set beforehand to be a reference for deciding thehigh lateral acceleration value (for example, 6.89 m/s²) With thelateral acceleration Gy being below 6.89 m/s², the execution just goesout of the routine and proceeds to S102.

[0042] On the other hand, when the lateral acceleration Gy is decided tobe 6.89 m/s² or above as being in high lateral acceleration running atS302, the execution goes to S303 where a decision is made as to whethera slip occurs at any one of the right and left rear wheels or not (forexample, whether a difference between a vehicle speed V and each of therear wheel speeds exceeds a threshold value set beforehand or not). Whenno slip occurs at any of the right and left rear wheels, the executionreturns to S302. When the slip occurs at any one of the right and leftrear wheels, the execution goes to S304.

[0043] With the decision made at S303 as the slip occurs at any one ofthe right and left rear wheels, the execution going to S304 carries outfront and rear braking force distribution control which adequatelydistributes braking force between the front and rear wheels for the rearwheel at which the slip occurs.

[0044] When the lateral acceleration Gy is in a high region setbeforehand, the above-described front and rear braking forcedistribution control, under a condition set beforehand, for example, isexecuted by selecting depending on the vehicle speed V either a selectlow control, which controls braking forces of the right and left wheelsin accordance with a wheel on the side with a large slipping state, orindependent braking control, which independently controls the brakingforce of each of the wheels depending on the slipping condition thereof.When the lateral acceleration Gy is in an intermediate region setbeforehand, the braking force distribution control is executed byselecting depending on the vehicle speed V and a longitudinalacceleration Gx either the select low control or the independent brakingcontrol. When the lateral acceleration Gy is in a low region setbeforehand, the braking force distribution control is executed byselecting the select low control.

[0045] The select low control and the independent braking control carryout control of pressure holding, pressure increasing and pressuredecreasing depending on, for example, a speed difference between thefront and rear wheels. By setting a threshold value for the pressureholding, a threshold value for the pressure decrease, and a thresholdvalue for the pressure increase beforehand, the braking pressure is heldwhen the speed difference between the front and the rear wheels becomesequal to or above the threshold value for the pressure holding, thepressure decrease control of the braking pressure is carried out whenthe speed difference becomes equal to or above the threshold value forthe pressure decrease, and the pressure increase control of the brakingpressure is carried out when the speed difference is below the thresholdvalue for the pressure increase.

[0046] Thereafter, the execution goes to S305 where a decision is madeas to whether the ABS control is operated at any one of the right andleft rear wheels or not. When no ABS control is operated at any of theright and left rear wheels, the execution returns to S302. When the ABScontrol is operated at any one of the right and left rear wheels, theexecution goes to S306.

[0047] The execution going to S306 stops the front and rear brakingforce distribution control for the other wheel without ABS controloperation and carries out a stepwise pressure increase control. Thestepwise pressure increase control provides a stepwise pressure increasefor the other wheel without ABS control operation up to a brakingpressure to be reached (for example, an estimated ABS operatingpressure), by finely repeating pressure increasing and holding only at astart of the control. After the stepwise pressure increase control, theexecution goes out of the routine.

[0048] Under the above-described braking control, an example ofvariation in a braking pressure with time at braking at a high lateralacceleration turning will be explained with reference to FIG. 6. In theexample, the surface condition of a road (for example, a road surfacefriction) is taken as being the same on the right wheel side and theleft wheel side of the vehicle.

[0049] First, a vehicle just going to be braked in turning normallybrings a turning inside wheel into a slipping condition easier than aturning outside wheel because the more vertical load of the vehicle istransferred to the turning outside wheel side. Thus, from a time t10 inthe diagram, the front and rear braking force distribution control iscarried out at the turning inside wheel to provide adequate braking.Then, at the time t11, a slip occurs on the side of the turning outsidewheel, where the front and rear braking force distribution control isalso carried out to provide an adequate braking operation.

[0050] Thereafter, with the time reaching a time t12, when the ABScontrol is operated at the turning inside wheel, the stepwise pressureincrease control is executed at the turning outside wheel to be executedfrom the time t12, by which a braking pressure is increased stepwise upto an estimated ABS operating pressure.

[0051] Then, with the time coming at a time t13, the ABS control isexecuted also at the turning outside wheel. Therefore, also in thesecond embodiment, no sudden impact due to a high vertical load iscaused when the ABS control is operated at the turning outside wheel toprevent the occurrence of unpleasant rolling behavior and allow anatural, reliable, and stable braking to be performed. Moreover, thiscan be applied by only changing the software side of a conventional ABScontrol, so that the realization thereof is allowed without anyparticular addition of complicated mechanism. Furthermore, since thefront and rear braking force distribution is executed before the ABScontrol, the tires do not lose grip forces to allow an adequate brakingto be performed in stable.

[0052] As explained above, according to the present invention, anatural, reliable, and stable braking is obtained by preventingunpleasant rolling behavior from occurrence without any particularaddition of complicated mechanism when turning with a high lateralacceleration in a vehicle which carries out braking control of each ofthe right an left wheels.

[0053] While there has been described what are at present considered tobe preferred embodiments of the present invention, it will be understoodthat various modifications may be made thereto, and it is intended thatthe appended claims cover all such modifications as fall within the truespirit and scope of the invention.

What is claimed is:
 1. A braking force control system of a vehicle,comprising: a lateral acceleration detecting unit detecting a lateralacceleration of the vehicle; and a braking control unit carrying out ananti-lock braking control and carrying out an independent brakingcontrol of right and left rear wheels, wherein, in a case that saidlateral acceleration exceeds a lateral acceleration value setbeforehand, when said anti-lock braking control is operated at one ofthe right and left rear wheels, said braking control unit executes astepwise pressure increase control for providing a stepwise pressureincrease for the other rear wheel up to a braking pressure to be reachedat a start of the control.
 2. A braking force control system of avehicle, comprising: a lateral acceleration detecting unit detecting alateral acceleration of the vehicle; and a braking control unit carryingout an anti-lock braking control and carrying out an independent brakingcontrol of right and left rear wheels, wherein said braking control unitexecutes a braking force distribution control between front and rearwheels as specified when said lateral acceleration exceeds a lateralacceleration value set beforehand, and said braking control unit stopssaid front and rear braking force distribution control of either one ofrear wheels and executes a stepwise pressure increase control thereofwhen said anti-lock braking control is operated at the other rear wheel,said stepwise pressure increase control providing a stepwise pressureincrease up to a braking pressure to be reached at a start of thecontrol.
 3. The braking force control system of a vehicle as claimed inclaim 2 , wherein said front and rear braking force distribution controlis started and executed depending on a slipping condition of the rearwheel.
 4. The braking force control system of a vehicle as claimed inclaim 2 , wherein said front and rear braking force distribution controlis executed by selecting one of a select low control controlling brakingforces of wheels in accordance with a wheel on the side with a largeslipping state, and an independent braking control independentlycontrolling the braking forces of the wheels depending on the slippingstate thereof in accordance with the lateral acceleration, alongitudinal acceleration and a vehicle speed.
 5. A braking forcecontrol method of a vehicle having a braking control unit carrying outan anti-lock braking control and carrying out an independent brakingcontrol of right and left rear wheels, said method comprising the stepsof: detecting a lateral acceleration of the vehicle; and executing, whensaid anti-lock braking control is operated at one of the right and leftrear wheels, a stepwise pressure increase control for providing astepwise pressure increase for the other rear wheel up to a brakingpressure to be reached at a start of the control, in a case that saidlateral acceleration exceeds a lateral acceleration value setbeforehand.
 6. A braking force control method of a vehicle having abraking control unit carrying out an anti-lock braking control andcarrying out an independent braking control of right and left rearwheels, said method comprising the steps of: detecting a lateralacceleration of the vehicle; and executing a braking force distributioncontrol between front and rear wheels as specified when said lateralacceleration exceeds a lateral acceleration value set beforehand; andexecuting, when said anti-lock braking control is operated at one of theright and left rear wheels, a stepwise pressure increase control of theother rear wheel after stopping said front and rear braking forcedistribution control thereof, said stepwise pressure increase controlproviding a stepwise pressure increase up to a braking pressure to bereached at a start of the control.
 7. The braking force control methodof a vehicle as claimed in claim 6 , wherein said front and rear brakingforce distribution control is started and executed depending on aslipping condition of the rear wheel.
 8. The braking force controlmethod of a vehicle as claimed in claim 6 , wherein said front and rearbraking force distribution control is executed by selecting one of aselect low control controlling braking forces of wheels in accordancewith a wheel on the side with a large slipping state, and an independentbraking control independently controlling the braking forces of thewheels depending on the slipping state thereof in accordance with thelateral acceleration, a longitudinal acceleration and a vehicle speed.